1. Field of the Invention
The present invention is related to a control device for a multi-phase DC-DC converter and related multi-phase DC-DC converter, and more particularly, to a control device and related multi-phase DC-DC converter device for systematically adjusting a channel current of a current converting channel by comparing a sensing signal of the current converting channel with a sensing signal of a previous converting channel to balance a channel current of each converting channel.
2. Description of the Prior Art
An electronic device includes various components, each of which may operate at a different voltage level. Therefore, a DC-DC (direct current to direct current) voltage converter is definitely required to adjust (step up or step down) and stabilize the voltage level in the electronic device. With the advancement of electronic technology, various electronic devices, such as a microprocessor in a personal computer, demand ever higher operating current. Thus, a multi-phase DC-DC converter formed with a plurality of parallelized converting channels is widely adopted by circuit designers. With multiple converting channels, ripples on input and output currents of the multi-phase DC-DC converter can be dispersed over the converting channels. In other words, the circuit designers can utilize smaller, cheaper filtering capacitors in the multi-phase DC-DC converter without sacrificing filtering performance of a traditional single-phase DC-DC converter.
Please refer to FIG. 1, which is a schematic diagram of a multi-phase DC-DC converter 10 of the prior art. The multi-phase DC-DC converter 10 mainly comprises a control circuit 100, a feedback module 102, current sensors 104_1, 104_2, 104_3, 104_4, and converting channels 110_1, 110_2, 110_3, 110_4. Compared to the traditional single-phase DC-DC converter, the multi-phase DC-DC converter 10 can provide a higher output current IOUT via the parallelized converting channels 110_1, 110_2, 110_3, 110_4. Note that each of the converting channels includes a power switch (112_1-112_4) and an output inductor (L_1-L_4), and a duty cycle of the power switches 112 is determined by a corresponding pulse width modulation (PWM) signal outputted by the control circuit 100, so as to produce a desired channel current (ICH[1]-ICH[4]). However, due to unpredictable manufacturing process variations or other factors, individual differences exist between the converting channels 110_1, 110_2, 110_3, 110_4, such that some of the converting channels are irrationally burdened with heavier current loadings. In other words, power components of each of the converting channels 110_1, 110_2, 110_3, 110_4 are burdened with unequal current loadings. For that reason, current bearing ability of the power components should be enhanced to ensure that the multi-phase DC-DC converter 10 can operate regularly. However, the stronger the current bearing ability, the more expensive the manufacturing cost. Even worse, if a minority of the converting channels were burdened with a majority of the overall current loading, heat would be concentrated at the minority channels, causing remarkable increases in operating temperatures of the power components of the minority channels, implying a shorter life of the power components. Therefore, the multi-phase DC-DC converter 10 has to adjust PWM signals PWM[1]-PWM[4], so as to balance current loadings of the converting channels 110_1, 110_2, 110_3, 110_4.
To balance the current loadings, the prior art has developed various methods for adjusting the PWM signals PWM[1]-PWM[4]. In detail, the current sensors 104 generate sensing signals SEN[1]-SEN[4] directly proportional to the channel currents ICH[1]-ICH[4] and sent to the control circuit 100. In addition, the feedback module 102 generates a feedback signal VFB sent to the control circuit 100 according to an output voltage VOUT of the multi-phase DC-DC converter 10. As a result, the control circuit 100 can adjust duty cycles of the PWM signals PWM[1]-PWM[4] based upon the sensing signals SEN[1]-SEN[4] and the feedback signal VFB, to balance the current loading of each converting channel. Please continue to refer to FIG. 2, which is a schematic diagram of the control circuit 100 shown in FIG. 1. The control circuit 100 includes parallelized comparators 200, 202, 204, 206, a comparison module 208 and a sawtooth wave generating module 210. The comparison module 208 and the sawtooth wave generating module 210 are respectively utilized for providing comparison results COMP[1]-COMP[4] and sawtooth signals RAMP[1]-RAMP[4] as input sources of the comparators 200, 202, 204, 206 respectively corresponding to the converting channels 110_1, 110_2, 110_3, 110_4 in accordance with the sensing signals SEN[1]-SEN[4] and the feedback signal VFB. As a result, the control circuit 100 can adjust the duty cycles of the PWM signals PWM[1]-PWM[4] by modulating the comparison results COMP[1]-COMP[4] and sawtooth signals RAMP[1]-RAMP[4]. For example, in U.S. Pat. No. 6,670,794 B1, the sensing signals SEN[1]-SEN[4] are current signals, and the sawtooth wave generating module 210 modulates the sawtooth signal of each converting channel by averaging the sensing signals SEN[1]-SEN[4], i.e.RAMP[1]=RMP[1]+k×(SENAVG−SEN[1])RAMP[2]=RMP[2]+k×(SENAVG−SEN[2])RAMP[3]=RMP[3]+k×(SENAVG−SEN[3])RAMP[4]=RMP[4]+k×(SENAVG−SEN[4])where RMP[1], RMP[2], RMP[3], RMP[4] respectively represent standard sawtooth signals of the converting channels 110_1, 110_2, 110_3, 110_4, k is a constant, and SENAVG=(SEN[1]+SEN[2]+SEN[3]+SEN[4])÷4 represents an average of the sensing signals SEN[1]-SEN[4].
In addition, in U.S. Pat. No. 6,897,636 B2, the sensing signals SEN[1]-SEN[4] are voltage signals, and the comparison module 208 modulates the comparison result of each converting channel by averaging the sensing signals SEN[1]-SEN[4], i.e.COMP[1]=CMP[1]+g×(SENAVG−SEN[1])COMP[2]=CMP[2]+g×(SENAVG−SEN[2])COMP[3]=CMP[3]+g×(SENAVG−SEN[3])COMP[4]=CMP[4]+g×(SENAVG−SEN[4])where CMP[1], CMP[2], CMP[3], CMP[4] respectively represent unmodulated standard comparison results of the converting channels 110_1, 110_2, 110_3, 110_4, and g is a constant.
However, regardless of whether the sensing signals SEN[1]-SEN[4] are current or voltage signals, the control circuit 100 has to include massive and complex circuits to perform the step of averaging the sensing signals SEN[1]-SEN[4], implying a remarkable increase in power consumption and circuit layout area of the multi-phase DC-DC converter 10. Therefore, balancing current loading of each converting channel in a simpler, more economical way has been a major focus of the industry.